The longterm objective of this research is to evaluate the neuroendocrine mechanisms by which hyperprolactinemia (hyperPRL) suppresses female reproductive function. The specific aims of this proposal are to test the working hypothesis that hyperPRL suppresses pulsatile and cyclic LH release by modulating opiatergic neuronal activity. We will assess whether this, in turn, influences the activity of catecholamine- containing neurons resulting in an altered pattern of GnRH release or whether opiates directly affect GnRH neurons. Furthermore, we will test two corollary hypotheses: (1) when hyperPRL does not affect LH, it is because the opiatergic/catecholamine/GnRH link is not functional in that endocrine milieu; and (b) if we restore the opiatergic/catecholamine/GnRH pattern, we can restore normal LH secretion, despite the presence of hyperPRL. Finally, we will test the hypothesis that hyperPRL compromises pituitary responsiveness. To test these hypotheses, we will (1) differentiate the circumstances under which hyperPRL does and does not suppress LH release; (2) examine how hyperPRL alters opioid neuronal tone; (3) assess whether hyperPRL- induced changes in opiate and catecholamine activity determine the efficacy of hyperPRL to suppress LH; and (4) determine whether hyperPRL decreases pituitary responsiveness to GnRH. We will assess opiate tone using 4 indices of activity: quantitation of opiate peptide concentrations in microdissected brain regions, monitoring of patterns of opiate peptide release into microdialysis probes placed in critical brain regions, measurement of opiate mRNA expression assessed using in situ hybridization, and autoradiographic quantitation of opiate receptor densities in key terminal areas. Three indices of catecholamine activity will be autoradiographic quantitation of adrenergic receptor densities. Patterns of GnRH release will be measured at the pituitary gland using dialysis methodology. Pituitary responsiveness will be measured in vivo and in vitro using the reverse hemolytic plaque assay in combination with in situ hybridization. Using this multifaceted approach, we should deepen the understanding of the neuroendocrine factors that regulate the pulsatile and cyclic release of LH and how hyperPRL perturbs this balance resulting in a different pattern of LH secretion.